1. Field of the Invention
The invention relates to a control apparatus for a power unit.
2. Description of Related Art
A power output unit that is provided with an internal combustion engine equipped with a catalyst that purifies components in exhaust gas discharged from a combustion chamber is described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A). This power output unit is configured to be capable of performing the control (this control will be referred to hereinafter as “engine start/stop control) of starting and stopping the operation of the internal combustion engine (this operation will be referred to hereinafter as “engine operation”). Besides, this power output unit starts or stops engine operation when the purification rate of the catalyst is higher than a certain predetermined value during the performance of engine start/stop control. However, if engine operation has already been started when the purification rate of the catalyst is equal to or lower than the aforementioned predetermined value during the performance of engine start/stop control, the power output unit prohibits the engine operation from being stopped and continues the engine operation. If engine operation has been stopped, the power output unit starts the engine operation, prohibits the engine operation from being stopped, and continues the engine operation.
One of the reasons why the power output unit described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A) performs the aforementioned control in accordance with the purification rate of the catalyst consists in preventing the emission properties of exhaust gas flowing out from the catalyst from deteriorating by suppressing a decrease in the purification rate of the catalyst. That is, since fuel is stopped from being supplied to the combustion chamber in stopping engine operation, combustion does not occur in the combustion chamber. On the other hand, however, gas is discharged from the combustion chamber. Accordingly, until a certain period elapses after the supply of fuel to the combustion chamber is stopped, a gas containing a large amount of oxygen is discharged from the combustion chamber, and the gas flows into the catalyst. Then, when this gas containing a large amount of oxygen flows into the catalyst, the catalyst may deteriorate. It should be noted herein that if the catalyst deteriorates when the purification rate of the catalyst is relatively low, it is impossible to sufficiently purify components to be purified by the catalyst when the exhaust gas containing the components flows into the catalyst.
However, in the power output unit described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A), when the purification rate of the catalyst is relatively low (i.e., when the purification rate of the catalyst is equal to or lower than the aforementioned predetermined time), engine operation is prohibited from being stopped. Therefore, the gas containing a large amount of oxygen is restrained from flowing into the catalyst, so that the catalyst is restrained from deteriorating. Thus, the emission properties of exhaust gas flowing out from the catalyst are prevented from deteriorating.
Meanwhile, the catalyst exerts its highest purification capacity when the temperature thereof is equal to or higher than a so-called activation temperature. Accordingly, in order to cause the catalyst to exert high purification capacity when exhaust gas flows into the catalyst, it is effective to hold the temperature of the catalyst equal to or higher than the activation temperature. In the power output unit described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A), the temperature of the catalyst is low. As a result, engine operation is started if the engine operation has been stopped when the purification rate of the catalyst is lower than the aforementioned predetermined value, and the engine operation is prohibited from being stopped and is continued if the engine operation has already been performed. Thus, when the purification rate of the catalyst is lower than the aforementioned predetermined value as a result of a low temperature of the catalyst, engine operation is performed, and exhaust gas at a relatively high temperature flows into the catalyst. Therefore, the temperature of the catalyst rises, so that the purification rate of the catalyst increases.
However, the start of engine operation and the continuation of the engine operation by the power output unit described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A) at the time when the purification rate of the catalyst is lower than the aforementioned predetermined value are the start and continuation that are not carried out when the purification rate of the catalyst is equal to or higher than the aforementioned predetermined value. Therefore, fuel is consumed correspondingly, and as a result, a deterioration in fuel economy is caused. Further, in the case where the power output unit is mounted on a vehicle and is designed to start and stop engine operation in accordance with a request made by a driver of the vehicle, if the power output unit starts engine operation as in the case of the power output unit described in Japanese Patent Application Publication No. 2004-124827 (JP-2004-124827 A) when the purification rate of the catalyst is lower than the aforementioned predetermined value, a sense of discomfort may be caused to the driver.